Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

• Published in: Annales Geophysicae
• Main Authors: A. Viljanen, E. Tanskanen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2011
• Subjects: Science; Q; Physics; QC1-999; Geophysics. Cosmic physics; QC801-809; Kilpisjärvi
• Online Access: https://doi.org/10.5194/angeo-29-1783-2011; https://doaj.org/article/2cd6717e03294d3fbb43d8ca4db776fa

We investigate the characteristics of rapid geomagnetic variations at high latitudes based on the occurrence of large time derivatives of the horizontal magnetic field ( d H / dt exceeding 1 nT s −1 ). Analysis of IMAGE magnetometer data from North Europe in 1983–2010, covering more than two solar cycles, confirms and specifies several previous findings. We show that d H / dt activity is high around the midnight and early morning hours, and nearly vanishes at noon and early afternoon. This happens during all seasons, although the midnight maximum is nearly invisible during summer. As indicated by modelled ionospheric equivalent currents, large d H / dt values occur predominantly during westward ionospheric electrojets. Before and around midnight, d H / dt tends to be north-south oriented, whereas in the morning hours, its direction is more west-east directed. d H / dt tends to be more strictly north-south oriented during winter than other seasons. The seasonal occurrence of large d H / dt values is similar to the variation of the maximum amplitude of westward equivalent currents. The yearly fraction of east-west directed large d H / dt vectors at the Kilpisjärvi station (MLAT 65.88) varies from 31 to 47 % without any clear correlation with the general geomagnetic activity nor with the yearly averages of solar wind parameters.